1. Field of the Invention
The invention relates to light source driving devices, and particularly to a light source driving device with a fault detecting function.
2. Description of Related Art
Conventionally, discharge lamps, such as Cold Cathode Fluorescent Lamps (CCFLs), External Electrode Fluorescent Lamps (EEFLs), need inverters. Normally, in order to protect the inverter, each inverter comprises a fault detecting circuit to detect whether the discharge lamps are faulty.
FIG. 6 is a conventional light source driving device with an fault detecting function. A power stage circuit 10 converts a received signal to an alternating current (AC) signal. The AC signal is converted to a sine-wave signal to drive lamps L11, L12 via a resonance circuit composed of a transformer T and a capacitor C. A current balancing circuit 11 is connected to the lamps L11 and L12, for balancing current flowing through the lamps L11 and L12 and outputting a current feedback signal. A fault detecting circuit 12 is connected to a low voltage end of a secondary winding of the transformer T, for detecting whether the lamps L11 and L12 are faulty and outputting a fault signal. A feedback control circuit 13 is connected between the current balancing circuit 11, the fault detecting circuit 12, and the power stage circuit 10, for controlling output of the power stage circuit 10 according to the current feedback signal and the fault signal.
In fact, the fault signal output from the fault detecting circuit 12 is a current signal transmitted to the low voltage end of the secondary winding of the transformer T via the current balancing circuit 11. However, the current signal may be attenuated by the current balancing circuit 11, and the attenuated current signal is what is detected by the fault detecting circuit 12 at the low voltage end of the secondary winding of the transformer T. Then, the fault detecting circuit 12 compares the attenuated current signal to a predetermined current signal, which leads to unreliable detection of faults. Therefore, the light source driving device can not exactly determine whether the lamps L11 and L12 are faulty.